Multiplex transceiving arrangement



Patented Oct. 2, 1951 2,570,010 MULTIPLEX TRANSCEIVING ARRANGEMENT Cornelis Johannes Henricus Antonius Staal, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Conn, as. trustee Company, Hartford,

Application February 18, 1948, Serial No. 9,167

In the Netherlands March 5, 1947 I 3 Claims.

This invention relates to a multiplex transceiving arrangement comprising a number of transmitting channels which are released periodically and successively by so-called gating-pulses and may be used for telephone or telex connections.

In such a device the transmission channels are periodically released for a short time during every system cycle by different pulses of the series of gating pulses occurring in a cycle.

These series gating pulses are used both at the transmitting side and at the receiving side and should be exactly isochronous, in connection with which usually one of the transmission channels is used for transmitting one synchronisation pulse per transmission cycle.

Hereinafter the repeater frequency of the transmission cycli and synchronisation pulses will be called the cycle frequency, the higher frequency by means of which the different transmission cycles are successively switched on being called the switching frequency.

In such a multiplex system it is known to transmit the signals by pulse-duration or pulse-phase modulation, it being customary to superpose at the transmission side each of the signals to be transmitted, for obtaining corresponding pulses modulated in duration or phase, on a sawtooth voltage of switching frequency, and to feed the voltage thus obtained to a threshold device, as a result of which pulses are obtained, of which the duration depends upon the signal in question. By differentiation of these pulses phase-modulated pulses are produced. If desired, a pulse generator may be used directly behind the threshold device, which generator suplies pulses of constant duration, thus obtaining pulse-phase modulation without using a differentiating network.

According to another known method for obtaining pulse-duration or pulse-phase modulation, the modulating voltage is first translated into a stepped voltage varying discontinuously with the time and this voltage is supplied to a threshold device after adding a sawtooth voltage of switching frequency.

It is not necessary that the aforesaid voltage which varies in a linear relationship with the time and will further be called mixing voltage, should have a frequency corresponding to the switching frequency. For instance, the mixing voltage may have a fundamental frequency corresponding to the cycle frequency (for instance Wireless World, June 1946, page 187 ff. Details of Armystation No.

The mixing voltages required in connection 2 q with the modulation-translation for the various channels may, in certain systems, be taken from a common sawtooth generator which is synchronised by the cyclus synchronisation pulses.

At the receiving side a voltage linearly varying with the time or a mixing voltage is used again for demodulation of the incoming pulses. For instance, pulses depending in duration upon the momentary amplitude of the signal to be transmitted, for suppressingthe influence of undesired extensions of the pulses, e. g. due to parasitic reflections or echo phenomena, after differentiation and subsequent limitation in amplitude and duration of the pulses, are multiplicatively mixed with a saw-tooth voltage, thus obtaining pulses with an amplitude varying in accordance with the transmitted signal.

In the event of impulse-phase modulation the incomingv pulses,-: after amplitude-detection for obtainingthe initial signal, can directly be mixed multiplicatively with the mixing voltage.

In this case also the required mixing voltages canbe generated by means of one or more sawtooth generators synchronised by the transmitted synchronisation pulses. I

The invention has for its object to simplify multiplex transceiving arrangements of this type, which simplification moreover affords particular advantages. 1

According to the invention, the mixing voltage required for each channel in transceiving arrangements of the kind referred to is obtained by integration of the gatingpulses by which the channel in question is periodically released.

The network used for integration of the gating pulses preferably has a time constant exceeding I the duration of a gating pulse (for instance two 1 to three times as great).

In using the invention sawtooth generators can be dispensed with and, moreover, an extremely exact coincidence between the gating pulses and the mixing voltages is naturally ensured; this is not the case in the conventional arrangements where it involves crosstalk and other disturbances. I

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, given by way of example, in whichFigs. 1 and 2 represent diagrams of a multiplex transmitting arrangement and a multiplex transceiving arrangement respectively.

The executional example given in Figure 1 represents a multiplex transmitter comprising nine transmission channels I to 9, of which the first channel I serves for the transmission of cyclesynchronisation pulses and the remaining channels constitute, for instance, conversation channels. At ID the input terminals are shown separately.

The transmission channels are alternately released, in the rhythm of the switching frequency, by gating pulses from a number of pulse modulators II to I9, the number of which corresponds with the number of channels and each of which supplies one of the pulses of a series of ating pulses. a

The series of pulse-generators are operated in the rhythm of the cycle frequency by a cycle synchronisation pulse which is supplied to the first pulse-generator I I through a lead and is taken from a pulse-generator 40 which is synchronised by a sinusoidal voltage of cycle-frequency' supplied by the oscillator 4|. Every time upon the occurrence of a cycle synchronisation pulse the pulse-generators I I to l9 excite each other in succession, termination of the gating pulsesbeing initiated by switching pulses supto all pulsegenerators. The last-mentioned pulses, which occur in the rhythm of the switchquency and duration but with a phase which depends upon the momentary amplitude of the low- ;frequency signal of the amplifiers 2 to 9. The gating pulse which serves as a'synchronisation pulse is amplified in the synchronisation channel I, 2|. The pulse modulators 22 to 29 and the j amplifier 2| are connected in parallel at the outplied through the lead 42 in parallel-connection put side and connected to an output terminal 30 which may be connected to the modulator for a carrier wave to be transmitted.

The pulse modulators may, for instance, each comprise an amplifying tube connected as a pulse generator and having two control grids to which the low-frequency signal and a mixing voltage linearly varying with time are supplied respectively, this tube acting at the same tim as a threshold device owing to a high negative bias on one of the control grids. The required mixing voltage linearly varying with the time is obtained, according to the invention, in each channel by integration of the gating pulses appearing in the channel'in question. To this end integrant networks 32 to 39 consisting of th series-connection of a resistance and a condenser are connected to the pulse generators I2 to l9. V I

To ensure suflicient linearity of the mixing voltage appearing atthe condensers of the integrant networks, the time constant of these networks is so chosen as to exceed the duration of a gating pulse so that, for instance with a (customary) amplitude of the gating pulses of to volts the amplitude of the mixing voltage may amount to 5 to 10 volts, which without amplification, will generally be sufiicient for the purpose aimed at, for instance with a maximum pulse mod- The condensers of the integrant networks 32 to 39 become discharged during the blocking time of the amplification channels I to 9 in question, which time materially exceeds the duration of a gating pulse and is consequently amply sufficient for ensuring a substantially complete discharge of the condensers with the said choice of the time constant.

Fig. 2 represents a multiplex reeciving device for receiving signals which are transmitted, for V duration, and on the other hand to a device 49 for separating synchronisation pulses and signal pulses which device may fundamentally consist of an integrant network.

The synchronisation pulses are supplied through the lead 59 to the first of a number of pulse-generators 52 to 59 corresponding with the number of channels, which generators excite each other in succession and each supply one of eight succeeding positive gating pulses which release successively the impulse-phase demodulators 62 to 69 that are included in the difierent receiverchannels and to which the incoming signal pulses are supplied in parallel connection through the lead 4-8. I p The mixing voltage linearly varying with time and required for impulse-phas demodulation is produced in each channel by integration of the gating pulses operative therein by means of integrant networks I2 to T9, and supplied to the impulse-phase demodulators 62 to B9. The obtained low-frequency signal voltages are supplied, if desired through the filters suppressing the impulse II to I9 in conjunction with channels I to 9 may be hadby reference to the copending application S. N. 9,165, filed February 18, 1948.

The diagram represented in Fig. 2 shows in detail the third receiving channel 64, 84 and associated gating pulse generator 54 of' the uniform receiving channels; this channel Will b explained more fully hereinafter.

The gating pulse generator comprises two pentodes 9|, 9| which are housed in a single tube and comprise separate anode-resistances interconnected suppressor grids and screen-grids and a common cathode. The pentodes are coupled crosswise by means of a condenser 93 and a resistance 93 so that they cut off one another mutually.

This arrangement which is known per seex- At the first working point, which will hereinafter be called the state of rest, the pentode 9| carries the maximum anode current and the pentode 9| is cut off. At the second working point the situation is reversed and the pentode 9| is cut off, whereas the pentode 9| carries current.

'15 Dueto'the crosswise coupling the changing over from one working point to the other occurs very rapidly. By applying a high positive bias to the control grid of the pentode 9| (across resistance 94) the pentode 9| will normally carry current, the voltage set up at a grid-resistance 94' of the pentode 9|, which grid-resistance, together with the coupling resistance 93' constitutes a voltage divider connected between the anode of the pentode 9| and earth, being insumcient for suppressing the cutting off of the pentode 9| which is caused by a cathode resistance preferably common to all pulse generators.

On termination of a gating pulse produced by a pulse generator 53 preceding the pulse generator 54 a negative pulse is supplied, through the coupling lead 95, to the control grid of the pentode 9|, which impulse causes the pulse generator 54 to tip over from the state of rest into the operative state. After a lapse of time substantially determined by the charging time of the coupling condenser 93 the pulse generator resumes automatically its state of rest, and at the same time a negative voltage pulse is produced by which the following pulse generator 55 is excited through the intermediary of a coupling condenser 96.

During the time in which the pulse generator 54 is not in the state of rest, a rectangular positive voltage impulse occurs at the anode resistance 92 of the pentode 9i, which impulse serves as a gating pulse for the third receiving channel and effects, through the coupling condenser 91, the release of the normally cut oil impulsephase demodulator 54.

The impulse-phase demodulator comprises a secondary emission tube 98 having a control grid to which the phase-modulated signal-pulses are supplied through the lead 48, it furthermore comprising a screen-grid which serves as a second control-grid and to which the gating pulses from the pulse generator 54 are supplied, a secondary-emission auxiliary cathode 99 which is connected to the positive anode voltage terminal I02 through an auxiliary cathode resistance IOI shunted by a condenser I00, and an anode I03, comprising an anode resistance I04.

In the impulse phase demodulator use is made of a special property of a secondary emission tube and more particularly the following: If the anode potential is lower than the auxiliary cathode potential, secondary electrons dislodged at the auxiliary cathode will for the greater part return to the auxiliary cathode so that a positive auxiliary cathode current is produced. If, however, the anode potential exceeds the auxiliary cathode potential, the secondary electrons leaving the auxiliary cathode will exceed in number those of the primary electrons impinging on this cathode and a negative auxiliary cathode current occurs. If the anode supply voltage used for the auxiliary cathode is lower than that which is used for the anode, and the auxiliary cathode lead comprises a resistance which is large in comparison with the anode resistance, a state of equilibrium is established owing to the aforesaid reversal of polarity of the auxiliary cathode current in such manner that the auxiliary cathode potential steadily attains a value practically correspondding to the anode potential. With a low time constant for the current carrying auxiliary cathode circuit the establishment of this state of equilibrium accordingly occurs rapidly. In the event of the tube being cut off, however, the potential of the auxiliary cathode will not be able to follow the anode potential in the case of variations thereof.

In the present case the aforesaid property explicitly described in patent application No. 711,689, filed November 22, 1946, is utilised for impulse-phase demodulation. From the gating pulse amixing voltage increasing linearly with the time during the gating pulse is derived by means of an integrant network 14. The mixing voltage thus obtained is supplied directly to the anode of the demodulating tube 98. By providing that the tube 98 carries current only with a signal impulse occurring during a gating pulse. the auxiliary cathode acquires the anode potential every time occurring during a signal pulse. and consequently acquires a potential which depends upon the phase of the signal pulse and is maintained, by the condenser I00 shunting the auxiliary cathode resistance IUI until the appearance of a following signal pulse. In this event the low-frequency signal having superposed on it a wave voltage of pulse-repeater frequency as a fundamental frequency is produced at the auxiliary cathode 99; however, the amplitude of this wave voltage is comparatively small so that it may, if desired, be suppressed-by a simple low-pass filter.

In the executional example the signal voltage set up at the auxiliary cathode 99 is supplied, through a condenser I05, to a pentode output amplifying tube I06 comprising an output transformer Illl, of which the secondary winding I08 is connected to the output terminal for the third receiving channel in question.

What I claim is:

1. In a communication multiplex system, transmitting apparatus comprising a plurality of pulse modulators each arranged to mix an intelligence signal with a saw-tooth voltage to produce a pulse having a characteristic depending on the instantaneous amplitude of said signal, a like,

plurality of transmission channels each coupled to feed said intelligence signal into a respective modulator, said channels being rendered sequentially operative at a predetermined periodic rate by rectangular gating pulses, means for generating said gating pulses including a like plurality of pu se generators each producing a rectangular pulse in response to an applied triggering voltage, said generators being connected in cascade relation whereby the actuation of the first generator in said cascade sequentially actuates the succeeding generators, means to apply a triggering voltage to the first generator in said cascade with a periodicity corresponding to said predetermined rate and means to apply the rectangular pulse developed by each of said generators to a respective channel to render same operative, an integrating network coupled to the output of each of said generators to convert the rectangular pulse produced therein into a sawtooth votage, means to apply said saw-tooth voltage to a respective modulator for mixing with the intelligence signal applied thereto, and a common output line connected to the outputs of said modulators whereby a train of pulses is formed during each sequential operation of the system.

2. In a pulse communication multiplex system,

transmitting apparatus comprising a plurality of pulse modulators each arranged to mix an intelligence signal with a saw-tooth voltage to produce a pulse having a characteristic depending on the instantaneous amplitude of said signal, a like plurality of transmission channels each coupled to feed said intelligence signal into a esnec i e modulator said; shanne s: eing r p:

dered sequen ly onera at a pr de e mm peri dicratebr rec n u gat ng u ses, means fereneratine; se dgating pu inc g a like plura ity f pul s er s ach Producing a rectangular pulse in response togan applied trig-1 gering voltage, said generators being connected n ascad e onh by he u i n of the. first: generator in; saidcascade v sequentially acmates: the succeeding generators, means: to apply a triggering voltage tothe first, generator in said cascade with a periodieityv corresponding to said" 7 rede erm n d; a e an a s p y e rec capsula muse loped by each of said en ra: tex s to ares cti e h n to nd r ame onerative, an integrating network coupled to the .3 Transmitting apparatus, as set forth in claim 2, wherein each of said rectangular pulse-genra s is c nstituted y an unbalanc d trigger circuit normally remaining in one equilibrium.

state and reverting to said state after a predetermined interval when triggered into another equilibrium state by an applied tri gering voltage, the trigger circuits being coupled in cascade relation such that each succeeding generator triggered. by the trailing edge of the rectangular pulse yielded in the preceding generator.

CORNELISV JOHANNES HENRICUS ANTONIUS STAAL.

7 REFERENCES CITED The following references are of record in theile of: h s pa en V UNITED STATES PATENTS Num er Name 7 Date 231 379 R eves --V ---==-.-..-r-- ,19 3%29374 Hou hton May 13, 1947 23291331 Labin Oct. 28, 1947 2,443198 Sallach", June 15, 1948" .34537 Grieg ----.V--+ ly 1 2&1233 flha teri a --V-- Ma 71948 

